The present invention relates to a novel process for the production of a coil of a hot rolled strip of austenitic stainless steel. Because the coil produced by the process of the invention already has recrystallization substantially completed and sensitization prevented, the subsequent annealing step may be omitted.
A coil of a hot rolled strip of austenitic stainless steel obtained by a conventional hot rolling process has a structure of not yet substantially recrystallized austenite and/or is in the so-called sensitized state. By the term "sensitized state," is meant that the coil contains carbides which have precipitated on grain boundaries or deformation bands in the course of slow cooling after coiling. Such a coil is hard and has a poor formability. Moreover it poses a problem as to the corrosion resistance which is inherent to stainless steel. Accordingly the coil is usually passed through a continuous annealing and pickling line, in which it is subjected to a heat treatment for the purposes of recrystallization annealing as well as dissolution of carbides and to a pickling process for the removal of scales, whereby a hot rolled stainless steel product or a material for cold rolling is produced.
The continuous annealing and pickling line is industrially very stable and is a large scale installation comprising an apparatus for solution treatment (generally comprised of a catenary annealing furnace maintained at a temperature of about 1100.degree. C. and a quenching device such as a spray cooler), an apparatus for descaling (such as a shot blast), two or three vessels for pickling, scrubbers, washers, a drier and a coiler. However, the continuous annealing and pickling line bears various economical and technical burdens. Since a coil which has been allowed to cool to ambient temperature is reheated to a temperature of about 1100.degree. C. to recrystallize and to dissolve carbides, considerable amounts of heat energy are consumed. When some parts of the line are stopped for some reasons, an overheating or an excessive pickling frequently may occur. Moreover surface defects may occur when the coil is uncoiled and carried by rolls through the reheating furnace.
If the annealing step can be omitted, the manufacturing process may be released from the above-mentioned various economical and technical burdens. In addition various advantages are expected including reduction in the total length of the production line, reduction in costs for installation and maintenance, and no need for stopping the line.